Generally, polyolefin resins are relatively inexpensive and have noteworthy properties such as chemical resistance, water resistance, heat resistance, etc., and therefore used in a wide variety of applications for automotive parts, electronic parts, building materials, food packaging films, and the like. However, since polyolefin resins having such remarkable properties are crystalline and non-polar, it is difficult to coat or bond products made of the resins.
Weakly chlorinated polyolefins exhibiting strong adhesion to polyolefin resins have been used as binder resins to coat or bond such low-adhesion polyolefin resins. For example, Japanese Examined Patent Publication No. 27489/1971 proposes an isotactic polypropylene chlorinated to have a chlorine content of 20 to 40 wt. % as a printing ink binder resin for polypropylene films. Japanese Examined Patent Publication Nos. 35445/1975 and 37688/1975 teach propylene-ethylene copolymers chlorinated to 20 to 40 wt. % as binder resins for printing inks and adhesives used on polyolefins.
Moreover, Japanese Examined Patent Publication Nos. 50381/1988 and 36624/1988 propose, as primers or binder resins for coating polyolefin molded articles, weakly chlorinated propylene-α-olefin copolymers with a chlorine content of 5 to 50 wt. % containing a carboxylic acid and/or carboxylic anhydride.
Generally, it is desirable to keep the chlorine content as small as possible since, as the chlorine content increases, such chlorinated polyolefins exhibit reduced solvent resistance and adhesion to polyolefins. However, when the chlorine content is excessively low, properties of the polyolefin solution are impaired, thickening or gelating during storage, thereby resulting in significant deterioration in coating workability during spray coating and the like. Even when the chlorine content of the chlorinated polyolefins is maintained within a range such that coating workability during spray coating and the like does not suffer, the chlorinated polyolefin solutions exhibit impaired flowability when stored at low-temperatures, thereby greatly limiting their handling properties at low temperatures such as in winter. Although it is possible to improve low-temperature flowability by keeping the concentration of the weakly chlorinated polyolefin in the solution low, when the concentration is excessively low, problems arise such as difficult pigment dispersion in solvents upon processing into inks and coatings, increased transportation cost, etc.
To overcome such problems, Japanese Unexamined Patent Publication No. 306227/1994 proposes a binder resin solution, as a binder resin solution composition with excellent low-temperature flowability, that is obtained by dissolving a weakly chlorinated polyolefin in an alicyclic hydrocarbon and aromatic hydrocarbon mixed solvent.
However, the use of such a mixed solvent requires complex process in production, resulting in high cost. Moreover, for example, when the mixed solvent is used as a part of the primer component for coating, upon blending with a solvent-dispersed resin, its low-temperature flowability is impaired due to the change in chemical composition of the solvent. Therefore, it is hardly a fundamental solution to the aforementioned problems.